As background art, Japanese Unexamined Patent Application, Publication No. HEI-10-133117 discloses a microscope equipped with a focal-point detection method, the so-called lateral shift method, in which a fixed pattern is projected onto an object to be detected, and a light beam forming an image of this pattern becomes asymmetric with respect to the optical axis in the vicinity of the pupil, so as to detect a variation in the gap between the object to be detected and an objective lens as a lateral shift of the pattern image.    [Patent Document 1]    Japanese Unexamined Patent Application, Publication No. HEI-10-133117.